At present, the 3D printer can print various objects, such as the small jewelry element or the large 3D house. The conventional 3D printer is controlled by a computer to move along a track which is a profile of an element having a predetermined shape. The conventional 3D printer performs a scanning to a liquid photosensitive resin, point by point and layer by layer, by adopting the ultraviolet laser. The scanned liquid resin layer generates a photo-polymerization to solidify and form one cross-sectional layer of an element. The layer by layer scanning is repeated continuously until the whole element is manufactured completely. The 3D printer controls movements of a reflector and a lens module via a control mechanism, and thus a movement of a focal point of a light beam can be controlled to realize a point by point printing. However, the 3D printer has a slower printing speed and a relative lower efficiency, therefore, it is difficult to realize a printing of an ultra-large scale workpiece.